The present invention relates to a multi-layer golf ball and methods for forming a portion thereof including a core having a center with at least one center layer, a mantle having at least one mantle layer of a resilient polymer component disposed concentrically about the center, a soft, thin intermediate layer disposed preferably between the center and the mantle, and at least one cover layer disposed concentrically adjacent the core. The invention also relates to the polymeric composition used in forming the intermediate layer. In another embodiment, the thin intermediate layer includes a responsive viscoelastic composition that exhibits an increase in viscosity under shear forces.
Generally, golf balls have been classified as solid balls or wound balls. Solid balls are generally comprised of a solid polymeric core and a cover. These balls are generally easy to manufacture, but are regarded as having limited playing characteristics. Wound balls are comprised of a solid or liquid filled center surrounded by tensioned elastomeric material and a cover. Wound balls generally have a good playing characteristics, but are more difficult to manufacture than solid balls.
The prior art is comprised of various golf balls that have been designed to provide optimal playing characteristics. These characteristics are generally the initial velocity and spin of the golf ball, which can be optimized for various players. For instance, certain players prefer to play a ball that has a high spin rate for playability. Other players prefer to play a ball that has a low spin rate to maximize distance. However, these balls tend to be hard feeling and difficult to control around the greens. Therefore, attempts to create a golf ball that couples the production ease of a solid ball with the beneficial playing characteristics of a wound ball, have been numerous.
A Japanese Publication No. 10127819 is directed towards a method for constructing a solid golf ball that provides a xe2x80x9csoftxe2x80x9d ball-hitting touch. The golf ball consists of a solid core of a three layer structure comprising an internal layer, an intermediate layer, and a cover layer, and a cover over the solid core. The internal layer of the three-layer structure is set to a JIS-C hardness of 40-90, the intermediate layer is made up of a thermoplastic resin composition to be set to a JIS-C hardness of 50-80, and the cover layer is set to a JIS-C hardness of 65 or more.
Another reference, U.S. Pat. No. 5,184,828 discloses a dual core golf ball whose core has a maximum hardness at the surface of the inner core and then increases in hardness from the surface of the inner core to the center of the inner core and from the surface of the inner core through the body of the outer core. Specific hardness ranges for each location are specified but the patent does not address the use of soft elastomeric film between layers.
Similarly, Japanese Patent Application No. 8-322964A of Kasco Corporation discloses a dual core ball whose core has an increasing hardness gradient, requiring that the inner surface of the outer core be harder than the remainder of the outer core.
The prior art additionally discloses a number of methods for the manufacture of golf balls employing a soft elastomeric film (such as a latex dip) on wound constructions. U.S. Pat. No. 5,733,428 discloses the use of latex dips within the body of a wound core to produce multilayer wound cores. The prior art also discloses the concept of a coating between the core and the outer cover of the ball; the coatings were comprised of fully-cured epoxy or other adhesive material to help increase core to cover adhesion.
However, none of these patents disclose or even suggest a nonwound, dual, multicore or liquid-center ball having the materials and material property requirements as disclosed herein, specifically the use of a soft, intermediate layer between the inner sphere and subsequent mantle layers, to provide the improved balls of the present invention. The softer, rubber interlayer can serve as a cushioning interface to improve the overall softness of the ball, as well as the fracture durability.
The present invention relates to a golf ball, and more particularly golf balls that have a multilayer core that provides improved playing characteristics by providing a cushioning interface between the center and any subsequent layers. The ball is comprised of a center; a soft, thin, elastomer latex intermediate layer around the center wherein the intermediate layer is less than about 0.01 inches thick and has a flexural modulus of less than about 10,000 psi; one or more mantle layers disposed concentrically adjacent the intermediate layer, wherein the mantle layer material comprises a resilient polymer component; and a cover layer disposed concentrically around the mantle.
Any soft, elastomeric latex or solution that will dry to form a soft film on the surface of the center or other subsequent mantle layers, can be employed as the intermediate layer. Typical thermosetting latex materials which can be used to coat the cores include low ammonia natural latex and/or pre-vulcanized natural latex. Natural latex is noted for its combination of high tensile strength, excellent elasticity, tack, low modulus, and ability to form strong, coherent, wet and dry films. Natural rubber latex is also relatively inert, nontoxic, cost effective, compatible with most core and outer shell rubber compounds, and can be air dried.
A preferred latex material is a partially pre-vulcanized natural latex that can be diluted with water to any solid content. It is understood that non-latex encapsulating materials may also be used. Such materials include elastomer adhesives as well as aqueous and non-aqueous adhesives, urethane dispersions, synthetic latexes, and alkyd resins. Other materials that could be suitable for the soft, intermediate layer, include aqueous acrylic and latex copolymers, and polyurethane coatings and preparations. The soft intermediate layer may also contain additives, fillers, thickeners, or a combination thereof, to adjust the specific gravity of the layer to alter various golf ball properties as needed or desired.
A natural rubber latex, when dried, is softer than either the inner or outer core compounds conventionally employed in golf ball manufacture. This property is particularly evident when the inner and outer core compounds are crosslinked and the latex is not. A soft rubber interlayer can serve as a cushioning interface to help improve durability and softness of the ball upon club impact. A soft rubber interlayer also serves to improve fracture durability, particularly when a strong adhesion between the center and mantle layers does not exist. In one embodiment of the present invention, the intermediate layer thickness is from about 0.0005 to 0.01 inches. Preferably, the intermediate layer thickness is from about 0.0008 to 0.01 inches. In another embodiment, the intermediate layer has a Shore A hardness of less than about 90. In a preferred embodiment, the intermediate layer has a Shore A hardness of less than about 70. Alternatively, the flexural modulus of the intermediate layer is less than about 3,000 psi.
The inner sphere, or center, may be of any dimension or composition, such as a thermoset solid rubber sphere, a thermoplastic solid sphere, wood, cork, metal, or any material known to one skilled in the art of ball manufacture. Preferably, the solid inner sphere is comprised of a resilient polymer such as polybutadiene, natural rubber, polyisoprene, styrene-butadiene, or styrene-propylene-diene rubber. Similarly, the inner sphere could be a fluid-filled sphere such as a rubber sack, a thermoplastic, or metallic shell design, in which the fluid could be of any composition or viscosity available to those of ordinary skill in the art. It is also feasible to construct such a center with a void or gas center. In one embodiment, the center has an outer diameter of about 0.5 to 1.50 inches. Preferably, the center outer diameter is about 0.75 to 1.25 inches. In another embodiment, the combination of the center, the soft elastic intermediate layer, and the mantle has an outer diameter of about 1.45 to 1.6 inches. Preferably, the combination of the center, the soft elastic intermediate layer, and the mantle has an outer diameter of about 1.5 to 1.58 inches. In another embodiment, the center can be filled with a fluid such as a liquid or a gas, a gel, or a cellular foam.
In still another embodiment, the intermediate layer is comprised of low ammonia natural latex and/or pre-vulcanized natural latex, elastomer adhesives, synthetic latexes, acrylic esters, alkyd resins, or mixtures thereof. Preferably, the soft intermediate layer is comprised of a natural or a synthetic latex.
In the current invention, a mantle comprising at least one layer, the layer comprising a resilient polymer component, is disposed concentrically around the intermediate layer. The mantle layer may contain a reinforcing polymer. Reinforcing polymer components, such as transpolyisoprene, block copolymer ether/ester, acrylic polyol, a polyethylene, a polyethylene copolymer, 1,2-polybutadiene (syndiotactic), ethylene-vinyl acetate copolymer, cyclooctene, trans-polybutadiene, and mixtures thereof, should have a glass transition temperature sufficiently low enough to avoid causing crosslinking or thermal degradation of the resilient polymer. Alternatively, the resilient polymer component of the mantle layer comprises polybutadiene, natural rubber, polyisoprene, styrene-butadiene, or styrene-propylene-diene rubber, or a mixture thereof. In one embodiment, the resilient polymer component of the solid center comprises polybutadiene, natural rubber, polyisoprene, styrene-butadiene, or styrene-propylene-diene rubber, or a mixture thereof. Preferably, the resilient polymer component comprises 1,4-cis-polybutadiene having a molecular weight average of about 50,000 to about 1,000,000. The amount of resilient polymer component of the mantle layer is between about 60 to about 99 weight percent of the total weight of polymer components. The mantle layer preferably has a flexural modulus of greater than about 3.5 MPa. Similarly, the golf ball further includes at least one of a filler, a free-radical initiator, or a crosslinking agent.
The present invention also provides a method for making a golf ball having a multi-layer core comprising forming an inner sphere; forming a soft, elastic, intermediate layer around the inner sphere wherein the intermediate layer is less than about 0.01-in thick and has a flexural modulus of less than about 10,000 psi; molding apart from the inner sphere and intermediate layer, and from elastomeric material two substantially hemispherical cups having substantially hemispherical cavities; placing the inner sphere and intermediate layer between the two cups within the cavities; joining the cups to form the golf ball core having an inner sphere, soft intermediate layer, and an outer layer; and forming a cover over the golf ball core.
In a first method, the soft, intermediate layer is formed over the inner sphere by a dipping method. The inner sphere is lowered into a bath of latex or other soft material that is of the correct viscosity and percent solids to leave a very thin layer of material, of substantially uniform thickness, encompassing the inner sphere. In a second method, the soft, intermediate layer may be applied by a spraying process in which the latex is applied through a nozzle, evenly coating the surface of the inner sphere.
Further, the molding of the cups preferably comprises compression molding first and second cups from the elastomeric material on opposite sides of a single mold part. The center, which has been coated with soft latex by a dipping or spraying process, is placed between the two cups, which are then joined at an elevated temperature, causing crosslinking there between, to form an outer layer of the core. Alternatively, the latex dip can be disposed on an inner cover layer of a golf ball. The step of joining the cups comprises adhesively attaching the cups to each other. When the cups are joined, the hemispherical cavities together form a spherical cavity, now occupied by the center or inner sphere, and the cups themselves form the outer layer of the core. Thus, the center is easily positioned concentrically within the finished ball. In another embodiment, the joining of the cups is achieved by compression molding. In still another embodiment, molding further comprises molding nonplanar mating surfaces on the cups adjacent the cavities, wherein joining the cups comprises meshing the mating surfaces.
Finally, a cover is molded around the core. Any process that results in accurate and repeatable central placement of the core within the cover is acceptable. Generally, covers are applied by compression molding, injection molding or casting cover material over the core.
The present invention further provides a golf ball, comprising a solid center having a first hardness; an intermediate layer formed over the solid center having a second hardness less than the first; an outer layer formed over the intermediate layer having a third hardness greater than the first hardness; and a cover. Preferably, the first hardness is between about 20 and 40 Shore D, the second hardness is less than about 20 Shore D, and the third hardness is greater than about 50 Shore D.
The invention also relates to a multi-layer golf ball including a core having at least one layer; a cover disposed concentrically about the core and having at least one layer; and an intermediate layer formed of a responsive viscoelastic composition disposed between the core and the at least one cover layer. The responsive viscoelastic composition includes at least one material that has a dilatant or thixotropic viscosity, i.e., exhibits an increase in viscosity in response to pressure such as shear forces.
In one embodiment, the intermediate layer is less than about 0.01 inches thick. In one preferred embodiment, the intermediate layer is from about 0.0005 to 0.01 inches thick. In one more preferred embodiment, the intermediate layer is from about 0.0008 to 0.002 inches thick.
In another embodiment, the intermediate layer is from about 0.01 to 0.1 inches thick. In one preferred embodiment, the intermediate layer is from about 0.01 to 0.03 inches thick.
In one embodiment, the intermediate layer is disposed between two cover layers. In another embodiment, the intermediate layer is disposed between the core and a second intermediate layer. In yet another embodiment, the intermediate layer has a plasticity of about 20 mils to 150 mils. In one preferred embodiment, the intermediate layer has a plasticity of about 60 mils to 120 mils.
In one embodiment, the intermediate layer includes a solid, semi-solid, gel, or gel-like material. In one preferred embodiment, the material can include at least one of polydimethyl siloxane, dimethyl cyclosiloxane, a hydroxy-terminated polydimethyl siloxane, polyvinyl alcohol, an acrylic plastisol, an acrylic organosol, a hydrocarbon-based gel, a sulfonate ionomer, butyl rubber ionomer, an ionized crosslinked polyacrylamide gel, a microporous fast-response gel, a thermoplastic elastomer gel, or a blend thereof. In particular, one suitable blend is a blend of at least one hydrocarbon-based gel with at least one sulfonate ionomer.
In one embodiment, the intermediate layer material has a-hardness of less than about 90 Shore A. In one preferred embodiment, the material has a hardness of less than about 70 Shore A. In one embodiment, the cover has a thickness of about 0.02 to 0.1 inches.